Microelectronic devices include processors, memory devices, RF devices, imagers and many other types of products. Microelectronic imagers are a growing sector of microelectronic devices used in digital cameras, wireless devices with picture capabilities, and many other applications. Cell phones and personal digital assistants (PDAs), for example, are incorporating microelectronic imagers for capturing and sending pictures. The growth rate of microelectronic imagers has been steadily increasing as the imagers become smaller and produce better images with higher pixel counts.
Microelectronic imagers include image sensors that use charged coupled device (CCD) systems, complementary metal-oxide semiconductor (CMOS) systems, or other solid-state systems. CCD image sensors have been widely used in digital cameras and other applications. CMOS image sensors are also very popular because they have low production costs, high yields, and small sizes. CMOS image sensors can provide these advantages because they are manufactured using technology and equipment developed for fabricating semiconductor devices. CMOS image sensors, as well as CCD image sensors, generally include an array of pixels arranged in a focal plane. Each pixel is a light-sensitive element that includes a photogate, a photoconductor, or a photodiode with a doped region for accumulating a photo-generated charge.
One problem with current microelectronic imagers is that they are sensitive to background electromagnetic radiation. Background radiation can indirectly influence the amount of charge stored at individual pixels by altering the amount of thermally emitted charges or “dark current” within the substrate material carrying the image sensor. This can affect the output from individual sensors in a manner that causes distortion of the image or a blackout of individual pixels. To overcome this problem, microelectronic imaging systems have incorporated EMI suppressing structures.
FIG. 1, for example, illustrates an existing imager assembly 10 having an EMI suppressing structure in accordance with the prior art. As shown in FIG. 1, the imager assembly 10 includes an imager die 12, an objective lens 20 attached to a first surface 14a of the imager die 12, a plurality of solder balls 15 attached to a second surface 14b of the imager die 12, and an encapsulant 22 encasing the objective lens 20 and the imager die 12. The imager die 12 typically includes a sensor array 16 (e.g., a CMOS or CCD sensor array) at the first surface 14a and a plurality of interconnects 18 extending between the first and second surfaces 14a-b to electrically connect the sensor array 16 and/or other internal circuitry (not shown) of the imager die 12 to the solder balls 15. As shown in FIG. 1, an existing EMI suppressing structure 30 includes a metal housing that has a cavity 25 in which the encapsulated imager die 102 and the objective lens 20 are positioned and an opening 26 aligned with the objective lens 20.
One drawback of the existing imager assembly 10 is that the EMI suppressing structure 30 is large and increases the footprint of the imager assembly 10. As shown in FIG. 1, the metal housing is larger than the imager die 12. Such a large footprint, however, is undesirable because cell phones, cameras, and other portable devices require smaller and smaller components.